1. Field of the Invention
The present invention relates to a metering feeder, and a system and method for kneading and extruding a material. In particular, the present invention is suitable for application to a material comprising a rubber composition (hereinafter referred to as “rubber material”).
2. Description of the Related Art
To knead a rubber material and render the rubber material uniform, a twin-screw kneading extruder is commonly used. In such a twin-screw kneading extruder, a pair of revolving screws are disposed adjacent to each other in a lateral direction so that a group of blades of one screw is partly engaged with that of the other screw. A rubber material is kneaded and conveyed by the pair of revolving screws, and the kneaded material is extruded through a die provided at the end. In addition to the use of this extruder, other various suggestions have been made.
For example, Japanese Unexamined Patent Application Publication No. 8-132433 discloses a technique for crushing bale rubber, kneading the crushed rubber, and continuously extruding the rubber. This technique includes a process having the steps of: supplying vulcanizable rubber to a conical-screw feeder; crushing and dynamically masticating the rubber in the conical-screw feeder; and extruding the rubber in a desired shape. This technique does not need the time and effort required for the use of a guillotine cutter or Banbury mixer; it provides a method with increased productivity at low cost, i.e., a method for processing bale rubber continuously, stably, and safely.
A manufacturing system is known in which a rubber block supplied from a first extruder for supplying a rubber block and an auxiliary material supplied from a second extruder for supplying an auxiliary material are metered to a continuous extruder for kneading both materials together. One known method for manufacturing a rubber composition by using such a manufacturing system is disclosed in Japanese Unexamined Patent Application Publication No. 11-262945. In this method, in order to accurately supply a rubber block to the continuous extruder, a pressure of 10 kgf/cm2 or more is applied to a conveyed rubber block immediately downstream of the tips of screws of the first extruder, i.e., at a head, where the highest pressure is applied to the rubber block, and the percentage of change in pressure at the head is held within 10%. According to this method, a rubber block is continuously supplied with stability, and therefore, a stable kneading can be performed in the continuous extruder.
When kneaded in a slightly compressed state, a high-viscosity material, such as rubber, is susceptible to a surging problem, which causes variable output, thus resulting in unevenness in quality. Therefore, the use of only a common kneading extruder is insufficient for ensuring consistent quality. For quantification and uniformity of a material, one known technique described above has a preprocessing step of crushing bale rubber and kneading the rubber by a conical-screw feeder; the other known technique kneads a rubber block and an additive together in a continuous extruder and controls the pressure. These features can improve the quantification and uniformity of a rubber material, but only a little. Therefore, a further improvement is required.